The invention relates to air induction systems for internal combustion engines. The invention is concerned particularly but not exclusively with such systems for multi-cylinder fuel-injection spark-ignition engines.
As engine management control systems become more sophisticated it becomes more important to be able to provide accurate control for the air flow rate into an engine, particularly when the engine is idling or operating with a very low load. The conventional kind of air control comprises a choke in an air flow passage leading to the engine and a throttle blade mounted in the choke and rotatable between a closed position transverse to the air flow direction and an open position parallel to the air flow direction. Some engines have more than one choke in which case the throttle blades may be mounted on a common spindle for movement in unison.
One problem which can arise in such a system is that for very small throttle openings the variation in air flow for a given throttle angle movement is too great to allow the required degree of sensitivity in the system as a whole. An object of the present invention is to provide a system which can give increased sensitivity, namely smaller changes in air flow for a given throttle movement at small throttle openings than with a conventional system.